In general, a Vuillemier cycle refrigerator is disclosed in a book titled "Cryocoolers Part 1: Fundamentals" (published by Plenum Press in 1983). Such a refrigerator, as shown in FIG. 1, includes a first cylinder 20 in which a hot displacer 2 is fitted. At an upper side and a lower side of the hot displacer 2, there are defined a hot space 4 and a first part 5A of an ambient space 5, respectively. The refrigerator also includes a second cylinder 21 in which a cold displacer 3 is fitted. At a right side and a left side of the cold displacer 3, there are formed a cold space 6 and a second part 5B of the ambient space 5, Respectively. The hot displacer 2 and the cold displacer 3 are connected to a crank mechanism 1 so as to be operated concurrently with a different phase. It is usual that a phase lag of 90 degrees is set between the hot displacer 2 and the cold displacer 3. The hot space 4 and the ambient space 5 are connected by a hot side regenerator or heat accumulator 7. The ambient space 5 and the cold space 6 are connected by a cold side regenerator or cooler 8. The foregoing elements except the crank mechanism 1 constitute a fluid circuit in which an operating fluid is filled. Helium gas or hydrogen gas is used as the operating fluid. Pressure fluctuations are produced by shuttling the operating fluid or gas periodically from the ambient space 5 to the hot space 4 by the action of the hot displacer 2. The pressure fluctuations produce refrigeration around the cold space 6 so as to absorb heat from a load 12 to be cooled. Thus, heat enters from the hot space 4 (cold space 6) and is derived to the radiator 11A (11B) for the ambient space 5.
In the foregoing structure, the displacements .xi. of the operating fluid in the heat accumulator 7 and the cooler 8 are illustrated in FIG. 2G and 2H, respectively, which are well-known. The pressure change of the operating fluid in each of the heat accumulator 7 and the cooler 8 is shown in FIG. 2I and is well-known. By combining FIG. 2G and FIG. 2I (FIG. 2H and FIG. 2I), FIG. 2E (FIG. 2F) can be obtained. It is to be noted in FIGS. 2A-2F the vertical axis denotes the pressure of the operating fluid, the positive direction of the horizontal axis denotes the decrease of the displacement .xi. of the operating fluid and each arrow along the line corresponds to one shown in FIG. 1.
Ideally speaking, in order to obtain high efficiency work (heat absorption) at the heat accumulator 7 (the cooler 8), in the heat accumulator 7, the operating fluid should be in heat-absorption with a pressure decrease or volume expansion at the hot space side and should be in heat radiation with a pressure increase or volume shrinkage at the ambient space side as shown in FIG. 2A. For the heat absorption in high efficiency, in the cooler 8, the operating fluid should be in heat-absorption with a pressure decrease or volume expansion at the cold space side and should be in heat radiation with a pressure increase or volume shrinkage at the ambient space side as shown in FIG. 2B. Comparing FIG. 2A with FIG. 2E (FIG. 2B with FIG. 2F), it is revealed that the conventional Vuillemier cycle refrigerator does not operate efficiently.
To realize the foregoing relationships illustrated in FIGS. 2A and 2B, the conventional Vuillemier cycle refrigerator should be such that the phase of the hot displacer 2 is substantially the same as that of the cold displacer 3. If such movements of the displacers 2 and 3 are established, phase lag does not occur between the change of the hot space 4 and the change of the cold space 6, resulting in less variation of the average temperature of the operating fluid. Thus, the pressure fluctuation becomes small. However, such structure is impractical. Contrary to the above, a phase difference of about 180 degrees between the hot displacer 2 and the cold displacer 3 will realize the maximum pressure fluctuation. Under such a situation, as seen from FIGS. 2C and 2D, no heat absorption and no heat radiation are established at each of the heat accumulator 7 and the cooler 8.